In the lighting field, LED lights are an increasingly preferred alternative to replace traditional light sources (e.g., halogen lamps). When using LED lights to replace halogen lamps, it may be necessary to match with electronic transformers in traditional circuits to ensure normal operation of the electronic transformers. Also, accurate dimming on the LED load may be required in order to maximize advantages of energy saving and high luminous efficiency of the LED light load.
In conventional approaches, a triac dimming scheme may be utilized for dimming an LED lamp load. In an LED driver with an electronic transformer, a triac dimmer is generally placed in front of the electronic transformer. Triac dimming can be used to adjust a supply voltage for the LED lamp load by controlling a triac conducting angle, so as to realize dimming. However, conventional LED drivers generally contain a large filter capacitor, which can cause current through SCR to be uncontrollable due to LC resonance in the circuit, possibly resulting in the SCR not being able to maintain conductivity. Therefore, the LED may appear as a strobe light. In recent years, a variety of control methods using SCRs for LED dimming have also been proposed. For example, a dummy load (e.g., resistors) may be added in order to improve controllability. However, such a dummy load may lower circuit efficiency due to power consumption on the dummy load.
In addition, electronic transformers in traditional circuits were originally designed for halogen lamp (instead of LED lights) loads, so electronic transformers typically require maintaining a minimum load current during normal operation. Therefore, in an LED driver with an electronic transformer, it is difficult to ensure that the LED driver not only meets requirements of electronic transformer minimum operating current, but also can achieve accurate dimming for an LED light load to avoid LED light flash or strobe effects, and to improve circuit efficiency.